The Development of a Transportable Humidity and Temperature Generator

This paper describes the development and testing of a transportable humidity and temperature generator primarily used for the calibration of humidity instrumentation in laboratories and on-site. The unit is capable of generating humidity and temperature environments over the ranges 0…60°C and 2…95%rh, and is fully selfcontained, requiring only an electrical supply. The design of both the temperature and humidity control systems are discussed, including how many of the inherent difficulties in achieving stable control in a small chamber have been overcome. Test methods and data are presented to show how the key performance issues of temperature control stability and temperature gradients can both be specified to be better than 0.1°C. Included is a presentation of an uncertainty budget, with worked examples based on probe and chilled mirror transfer standards.